This invention relates to a tire pressure gauge and particularly to a pressure gauge which is attached to an inflating valve of a tire only at the time of measuring the pressure in the tire.
The pressure gauge of the above-mentioned type is known in the art. U.S. patent application No. 07/216,373 which is owned by the applicant of this application discloses a pressure gauge shown in FIG. 1 which has has an outer casing D with a window and a transparent inner casing C, the inner casing confining a pressure chamber and accommodating a pressure responsive piston member B which carries a scale member A that can be viewed through the window of the outer casing and the transparent casing. The defects found in this pressure gauge are that: the device is most likely to create inaccurate results since the pressure in the pressure chamber is liable to leak through the sealed joints of the outer and inner casings; and the piston is subjected to much friction when sliding along the inner surface of the inner casing which is made of plastic.
U.S. Pat. No. 4,768,460 discloses a pen-like pressure gauge which includes an outer casing accommodating a tubular piston member which is integrally connected with a tubular scale member and in which the spring which urges the piston member must endure considerable force created by the weights of the piston and the scale member and thus is liable to be fatigued. Additional elements are provided in this pressure gauge to adjust the force of the spring in case of fatigue failure of the spring. This construction is rather complicated.